<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=\, initial-scale=1.0">
    <title>Document</title>
    <style>
        ul {
            list-style: none;
            padding: 0;
            margin: 0;
        }

        body {
            background: #23384e;
            font: 12px/1.5 \5fae\8f6f\96c5\9ed1;
        }

        .search,
        .search .inner-box,
        .search .box,
        .search .select,
        .search a {
            background: url(../images/search.jpg) no-repeat;
        }

        .search,
        .search .box,
        .search .inner-box {
            height: 34px;
        }

        .search {
            position: relative;
            width: 350px;
            margin: 10px auto;
        }

        .search .box {
            background-position: right 0;
            background: pink;
            border-radius: 20px;
        }

        .search .inner-box {
            background-repeat: repeat-x;
            background-position: 0 -34px;
            margin: 0 20px 0 40px;
        }

        .search .select {
            float: left;
            color: #fff;
            width: 190px;
            height: 22px;
            border: none;
            cursor: pointer;
            margin-top: 4px;
            line-height: 22px;
            padding-left: 10px;
            background-position: 0 -68px;
        }

        .search a {
            width: 80px;
            height: 24px;
            color: #333;
            letter-spacing: 4px;
            line-height: 22px;
            text-align: center;
            text-decoration: none;
            background-position: 0 -90px;
            margin: 4px 0 0 10px;
        }

        .search a:hover {
            color: #f60;
            background-position: -80px -90px;
        }

        .search ul {
            position: absolute;
            top: 26px;
            left: 40px;
            color: #fff;
            width: 198px;
            background: #2b2b2b;
            border: 1px solid #fff;
            display: none;
        }

        .search ul li {
            height: 25px;
            line-height: 24px;
            cursor: pointer;
            padding-left: 10px;
            margin-bottom: -1px;
            border-bottom: 1px dotted #fff;
        }

        .search ul li:hover,
        .search ul li.active {
            background: #8b8b8b;
        }
    </style>
</head>
<body>
    <div class="search">
        <div class="box">
            <div class="inner-box">
                <input type="text" id="keyword" class="select" autocomplete="off" placeholder="请选择游戏名称">
                <a href="#">搜索</a>
            </div>
        </div>
        <ul class="list">
            <li>地下城与勇士</li>
            <li>魔兽世界（国服）</li>
            <li>魔兽世界（台服）</li>
            <li>热血江湖</li>
            <li>大话西游II</li>
            <li>QQ幻想世界</li>
        </ul>
    </div>
    <script>
         /*
            实现的功能：
                【1】搜索框获取焦点的时候 显示下拉下单
                    【1】获取元素
                【2】搜索框失去焦点时候 隐藏下拉菜单

                一下两个功能只有在获取焦点的时候才会有用
                【3】按下鼠标的上下键 可以动态选中 li元素（给li元素添加 active 这个class名）
                【4】当按下 enter键的时候，把拥有 activeclass名的元素的内容 赋值给搜索框
         */
        var input = document.querySelector('#keyword')
        var list = document.querySelector('.list')
        var li = document.querySelectorAll('.list li')
        input.onfocus = function(){
            // 显示下拉列表
            list.style.display = 'block'
           
            // 按下    
            list.addEventListener('mousedown',function(e){
                e = e || window.event
                // 排他思想
                li.forEach(function(item,index){
                    item.className = ''
                })
                // 按下高亮
                e.target.classList.toggle('active')
                // 把值付到input
                input.value = e.target.innerHTML
            })
            // 键盘事件
            input.addEventListener('keydown',function(e){
                    e = e || window.event
                    var slot = undefined
                    li.forEach(function(item,index){
                        if(item.className == 'active'){
                            slot = item
                        }
                        item.className = ''
                    })
                    switch(e.keyCode){
                        case 38 :
                            // 如果 高光到顶部把高光换到底部
                            if(slot == undefined){
                                slot = list.lastElementChild
                                slot.className = 'active'
                                input.value = slot.innerHTML
                            }else{
                                // 把他上一个兄弟元素变成高光
                                slot = slot.previousElementSibling 
                                slot.className = 'active'
                                input.value = slot.innerHTML
                            }
                            
                        break
                        case 40 :
                            if(slot == undefined){
                                    slot = list.firstElementChild
                                    slot.className = 'active'
                                    input.value = slot.innerHTML
                                }else{
                                    slot = slot.nextElementSibling 
                                    slot.className = 'active'
                                    input.value = slot.innerHTML
                                }
                        break
                        // 换回车关闭下拉菜单
                        case 13 :
                            list.style.display = 'none'
                            input.blur()

                    }
                })
        }
        // 失去焦点关闭下拉菜单
        input.onblur = function(){
            list.style.display = 'none'
        }
        
    </script>
</body>
</html>